Improved immune response against HIV-1 Env antigen by enhancing EEV production via a K151E mutation in the A34R gene of replication-competent vaccinia virus Tiantan.

The development of an effective HIV-1 vaccine is still a global priority. In recent years, vaccinia virus (VV) has been widely used as an HIV-1 vaccine vector, but its immune efficacy against HIV-1 antigens needs to be optimized. The extracellular enveloped virus (EEV) of VV is capable of faster entry, earlier release, and long-range dissemination. We hypothesized that an improvement in EEV formation by the manipulation of VV genes involved in the EEV release would consequently cause an improved expression of the VV carrying HIV-1 Env antigen and a subsequent enhanced immune response. To this end, an A34R K151E mutant (rVTT-A34R) from VV Tiantan strain (VTT) with robustly increased EEV release was selected to serve as an optimized vaccine vector. The results were consistent with our hypothesis: the A34R mutant-based HIV-1 vaccine candidate rVTT-A34R-Env produced more HIV-1 Env antigen in vitro and in vivo, and thus led to an improved HIV-1 Env-specific T cell immune response, binding antibody, and even the neutralizing antibody response in mice without increased virulence. Meanwhile, the application of the A34R mutation on another VV-based HIV-1 vaccine candidate, VTKgpe, also exhibited a similar immune enhancement effect with no enhanced virulence. The results in this study suggested that rVTT-A34R is a potentially improved vaccine vector candidate for human application. In addition, the improvement of the EEV formation via the A34R gene mutation may also be potent in other poxvirus vector-based vaccines against HIV-1 or other pathogens and even cancer in the future.